Stock-Based Compensation (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
ESPP
Share-based compensation
Risk-free interest rate (as a percent)	0.10%	0.14%	0.18%
Expected life	6 months	6 months	6 months
Expected volatility (as a percent)	51.00%	42.00%	46.00%
Weighted average fair value per share (in dollars per share)	$ 15.89	$ 9.76	$ 6.25
Stock Options Plans
Share-based compensation
Risk-free interest rate (as a percent)	0.78%	1.92%	2.06%
Expected life	4 years 6 months	4 years 4 months 24 days	4 years 4 months 24 days
Expected volatility (as a percent)	50.00%	53.00%	55.00%
Weighted average option fair value (in dollars per share)	$ 20.32	$ 15.77	$ 13.12
Restricted stock awards
Share-based compensation
Expected life	3 years	3 years	3 years
Weighted average fair value per share (in dollars per share)	$ 42.91	$ 32.75	$ 29.92